Conventionally, as disclosed in Patent Literatures 1 and 2 listed herein below, a vehicle is known where a two-wheel drive state and a four-wheel drive state are switchable. Such a vehicle can be switched between the four-wheel drive state (hereinafter also referred to as a four-wheel drive mode) suitable for running on a rough road and the two-wheel drive state (hereinafter also referred to as a two-wheel drive mode) suitable for improving an energy consumption rate (in an internal combustion engine, a fuel consumption rate).
Specifically, each vehicle in the above Patent Literatures is a four-wheel drive vehicle that is basically an FF (front-engine front-drive) type, which includes a front side connection/disconnection mechanism to connect/disconnect torque transmission between a front differential and a propeller shaft, and a rear side connection/disconnection mechanism to connect/disconnect torque transmission between the propeller shaft and a rear differential. When traveling in the four-wheel drive mode, the respective connection/disconnection mechanisms are connected so as to transmit engine torque to rear wheels via the propeller shaft and the rear differential. On the other hand, when traveling in the two-wheel drive mode, the respective connection/disconnection mechanisms are released (disconnected) so as to stop the rotation of the propeller shaft during travel by not transmitting the engine torque and rotation force of the rear wheels (rotation force where the rear wheels are rotated by friction with a road surface) to the propeller shaft while being in the two-wheel drive state using only the front wheels. Thus, fluctuation or noises generated by the rotation of the propeller shaft are reduced. Also, the fuel consumption rate is improved by reduction of power loss.